The present invention generally relates to ink-jet printing, and in particular to a specific dye and ink sets for improving ink-jet print quality.
Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on a print medium in a particular order to form alphanumeric characters, area-fills, and other patterns thereon. Low cost and high quality of the hardcopy output, combined with relatively noise-free operation, have made ink-jet printers a popular alternative to other types of printers used with computers. Notwithstanding their recent success, intensive research and development efforts continue toward improving ink-jet print quality. A surge in interest in ink-jet printing has resulted in the need to produce high quality prints at a reasonable cost. The challenge remains to further improve the print quality and lightfastness of ink-jet prints. The emerging use of ink-jet prints for digital photos, requires high-resolution images that have accurate color and are durable.
Color ink-jet printers, such as a DesignJet(copyright) 10 ps printer available from Hewlett-Packard Company, typically use three inks of differing hues: magenta, yellow, and cyan, and optionally black. The particular set of colorants, e.g., dyes, used to make the inks is called a xe2x80x9cprimary dye set.xe2x80x9d A spectrum of colors, e.g., secondary colors, can be generated using different combinations of the primary dye set. In printing processes such as lithography, dye transfer, and some types of thermal transfer, it is possible to vary spot size so that less is demanded of the primary colored inks when producing a good secondary color. When the color inks are used in a binary printing device, that is, one in which a dot of color is either present or absent, e.g., a thermal ink-jet printer, the ability of the primaries to give recognizable secondary colors is even more important. When such device is to be used for printing images that will also be printed and compared to images printed by other modalities such as offset presses or dye sublimation printers, it is important that the colors produced by the inkjet printer are capable of encompassing and matching commonly accepted industry color descriptions, such as the color gamut (color space) for a Kodak Duralife(copyright) silver halide print. If such ink is to be used in an ink-jet printing device, characteristics such as crusting, long-term stability, and materials compatibility must also be addressed. If the ink is to be used in a thermal ink-jet printer, the further constraint of being thermally stable (kogation-resistant) is added.
In general, a successful ink set for color ink-jet printing must be compatible with the ink-jet pen and the printing system. Some of the required properties for the ink-jet ink include: good crusting resistance, good stability, the proper viscosity, the proper surface tension, little color-to-color bleed, rapid dry time, no deleterious reaction with the printhead components, high solubility of the dyes in the vehicle, consumer safety, low strike through, high color saturation, good dot gain, and suitable color characteristics. Furthermore, the durability of the printed image, e.g., light and water fastness, plays an important role in the quality of the printed ink-jet image.
Any given perceived color can be described using any one of the color spaces, such as CIELAB, and Munsell, as is well known in the art. For example, in the Munsell color space a given color is defined using three terms, Hue (H), Value (V), and Chroma (C). In the CIELAB color space, a color is defined using three terms L*, a*, and b*. L* defines the lightness of a color, and it ranges from zero (black) to 100 (white). The terms a* and b*, together, define the hue. The term a* ranges from a negative number (green) to a positive number (red). The term b* ranges from a negative number (blue) to a positive number (yellow). Additional terms such as hxc2x0 (hue angle) and C* (chroma) are used to further describe a given color, wherein
hxc2x0=tanxe2x88x921b*/a*xe2x80x83xe2x80x83EQUATION 1
C*=(a*2+b*2)xe2x80x83xe2x80x83EQUATION 2
The L*, a*, and b* or the Munsell H, V, and C can be used to calculate the volume of space that a specific dye set can producexe2x80x94the larger the volume the more colors the dye set is capable of producing.
Inks are known which possess one or more of the foregoing properties. However, few inks are known that possess all the foregoing properties, since an improvement in one property often results in the degradation of another property. Thus, many inks used commercially represent a compromise in an attempt to achieve an ink evidencing at least an adequate response in each of the foregoing considerations. For example, inks are known which can obtain the color gamut of silver halide prints, such as those used obtained in photographic prints, but cannot obtain the lightfastness of such silver halide prints. This shortcoming of these known inks is a poor lightfastness associated with the magenta and magenta-containing colors. Accordingly, investigations continue into developing ink formulations which have improved properties and which do not improve one property at the expense of the others. Thus, there remains a need in the art to further improve the print quality, color gamut, and lightfastness of the ink-jet prints without sacrificing pen performance and reliability, particularly when trying to reproduce the color gamut of silver halide prints.
In accordance with the invention, inks suitable for use in ink-jet inks and method for formulating the same are provided. A specific dye set for formulating the yellow, cyan, magenta, and black inks is disclosed, comprising Direct Yellow 132, at least one other yellow dye, a cyan ink comprising Direct Blue 199, magenta ink comprising dye having the structure: 
and, optionally, Pacified Reactive Black 31, respectively. This dye set provides excellent ink-jet prints having excellent lightfastness when exposed to office light, excellent imaging onto glossy inkjet media, and large color gamut which substantially encompasses the color space for a Kodak Duralife(copyright) silver halide reference print. In the practice of the invention, the yellow, cyan, and magenta aqueous inks each comprise from about 0.1 to about 5 wt % of at least one dye with the black ink comprising from about 1 to about 10 wt % of at least one colorant; from about 5 to about 20 wt % of at least one organic solvent; 0 to about 1.5 wt % of at least one component independently selected from the group consisting of surfactants, buffers, biocides, and metal chelators; and the balance water.
The present ink compositions offer good lightfastness and excellent color gamut that substantially encompass the color gamut volume of a silver halide reference print, and are reliable in an ink-jet printing engine.